Okra Pests, Disease and Weed management

Okra

James Mwangi Ndiritu

Environmental Governance and Management, Agribusiness consultant

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How do you control pests in okra?

Insects

Various insect species can be present in okra plants, but not all are harmful. Aphids and mites can cause damage, but growers can prevent this through frequent inspection. Frequent harvests can remove corn earworm eggs, making it less of a problem. Stink bugs and leaf-footed bugs can cause damage to the pods, making them unappealing to some markets.

Foliage feeders only cause significant economic damage when their numbers are high or when plants are young or stressed. Established and healthy plants can tolerate considerable foliage loss without yield loss. Young plants are more susceptible to foliar feeding damage and should be regularly checked for insects and feeding. Control may be needed if moderate feeding damage is observed on young plants. The main foliage-feeding insect pests of okra are listed below.

There are many insect pests which may attack okra, but among those most likely to be troublesome are silver leaf whitefly, cutworms (Heliothis amigera), rough bollworms and looper caterpillars, and green vegetable bugs. The insect pests of okra can be categorized into two groups: foliage feeders and pod feeders.

  • Silver leaf whitefly: okra appears to be one of its favoured hosts. Although there are chemicals which will assist with control of this pest, they should only be used under strictly supervised conditions as the insect will quickly develop resistance.
  • Tiny, dark, very active flea beetles which eat many small, round holes in leaves (shot holes).
  • Blister beetles with narrow necks and soft, elongated bodies about 1/2 to 3/4 inch long, which eat both foliage and blossoms.
  • Various caterpillars (such as loopers), which eat holes in leaves.
  • Aphids, which damage plants by sucking juice from the foliage.
  • Corn earworms, which chew holes and tunnel into pods.
  • Stink bugs and leaf-footed bugs, which suck juices from both the blossom and pod, causing small, dark, raised blister-like spots on the pod. Feeding on very young pods results in twisting and distortion of the pods.

 

Pod-feeding insects pose a more significant threat than foliage feeders because damage to the pods or flowers directly affects the edible portion of the plant. As soon as flowering and pod set occur, regular inspection of flowers and pods should be conducted to check for insects and feeding damage.

Insect control

Correct, insect control in okra can be challenging due to limited registered insecticides and varying effectiveness against different pests. Monitoring the crop regularly and using cultural controls are important for early pest detection and prevention.

To minimize insect damage to okra, growers should ensure that plants have favourable growing conditions, including sufficient water and fertilizer. Removing debris and weeds after harvesting will also reduce infestations in the following season. Weed control during the season around and in the field will reduce populations of many pest species. Early planting will reduce damage by several caterpillar species, and protective row covers can be used to shield young plants from insect feeding.

Regarding chemical controls, there are limited options for insecticides registered for okra due to the crop’s minor status and the high costs of registration. As a result, cultural and scouting practices are crucial for insect control.      

Nematodes  

Okra is highly vulnerable to damage from root-knot nematodes, which can cause stunted growth and reduced yields. Plants damaged by these nematodes will have round swellings on their roots. Planting okra in areas with high nematode populations should be avoided, but if necessary, a nematicide should be used before planting while following product guidelines. However, if it must be grown in such areas, a nematicide should be applied before planting while adhering to all product recommendations and restrictions.

Nematicides are essential if the soil is infested with nematodes. The incidence of Fusarium wilt is much greater when root-knot nematodes are present.

How nematodes can be controlled?

Non-chemical methods for managing nematodes include soil solarization, crop rotation, and the use of nematode-suppressive crops. Soil solarization uses heat from the sun to reduce nematode populations, and can also control weeds. Crop rotation is effective in controlling nematodes, and okra or related crops should not be planted in the same spot more than once every three years. Planting maize or small grain crops in rotation can also help reduce nematode populations. Nematode-suppressive crops can be used as an alternative to synthetic nematicides or long crop rotations by naturally releasing compounds that are toxic or inhibitory to nematodes.

Nematode control is a major practice in reducing Fusarium wilt presence. Root-knot nematodes (Meloidogyne species) cause severe galling on okra roots. Infested soil should be treated with a registered nematicide before planting. Crop rotations are an important management tool in preventing build-up of nematodes or other soil-borne organisms.

Below there is an indication regarding the active ingredients that can be used for pest control:

Pesticides used in Okra production

 The information in this section is provided for educational purposes only. Product trade names have been used for clarity, but reference to trade names does not imply endorsement by the author; discrimination is not intended against any product. The reader is urged to exercise caution in making purchases or evaluating product information. Label registrations can change at any time. Thus the recommendations may become invalid. The user must read carefully the entire, most recent label and follow all directions and restrictions. Purchase only enough pesticide for the current growing season.

Important Pesticide Precautions

  1. Observe all directions, restrictions and precautions on pesticide labels. It is dangerous, wasteful and illegal to do otherwise.
  2. Store all pesticides in original containers with labels intact and behind locked doors. Keep pesticides out of reach of children.
  3. Use pesticides at the correct label dosage and intervals to avoid illegal residues or injury to plants and animals. 
  4. Apply pesticides carefully to avoid drift or contamination of non-target areas.
  5. Always wear protective clothes when handling, mixing and spraying pesticides.
  6. If the pesticide is spilt on the skin or in the eyes, wash it off immediately with clean water and soap.
  7. Surplus pesticides and containers should be disposed of per label instructions so water contamination and other hazards will not result through burying and not throwing away. 
  8. Follow directions on the pesticide label regarding restrictions as required by Laws and Regulations  

How do you control diseases in okra?

Infectious diseases significantly impact the production of vegetables. Some of the most common fungal infections of okra are presented below.

Blossom blight

The most common disease of okra is blossom blight caused by the fungus Choanepbora cucurbitarum. Blossoms and sometimes small pods are covered with a cottony growth tipped with black fungal fruiting bodies. These pods fail to develop. The disease is more severe during periods of very high humidity, which is often the entire growing season. It is also found in vigorously growing okra, particularly in partial shade.

There are no effective fungicides approved for use on okra. The best control would be to avoid over-fertilization and planting in low areas or shady sections of a field. Also, avoid the use of overhead irrigation late in the day. Use overhead irrigation early in the day, allowing plants to dry off before night.

Yellow vein mosaic

This is a common disease in okra, which shows vein clearing and vein chlorosis of leaves. The yellow network of veins is very conspicuous, and veins and veinlets are thickened. Fruits become small and yellowish-green in colour. Whitefly (Bemisia tabaci) and leafhopper (Amrasca biguttula) are vectors of this virus.

Hence, their control is essential. The use of resistant varieties and destruction of host weeds (Croton sp and others) are also effective.

Seed Rot, Damping Off

Okra is very susceptible to a range of seedling diseases especially when grown during cool periods for which it is not well adapted. Using transplants rather than direct seeding can reduce losses in the field, although transplant losses can be very high unless vigorous sanitation is practised.

Plant fungicide-treated seed (Thiram) and use Apron, which is used for improved control of Pythium. Planting okra in warm soil that is well drained is critical. Cover crops should be turned under early to ensure they are well-rotted before planting.

Anthracnose and Fruit rots. 

The anthracnose causes spotting during wet weather and advances into the fruit. No fungicides are labelled for spraying on the fruit and foliage. Take steps to aid the drying of the fruit, such as avoiding low wet areas and fog pockets; do not plant okra between taller bordering plants such as maize. Removing several larger upper leaves to aid sunlight penetration and air circulation is also helpful.

Fusarium Wilt and Verticillium Wilt. 

Infected plants are stunted, have yellowing leaves, and show vascular discolouration in the stem. A general soil fumigant should be considered in fields with a history of these diseases. Avoiding solanaceous crops in the rotation (potatoes, cotton, tomatoes, tobacco, eggplant, and peppers). Conversely, okra can build high populations of Verticillium, causing serious problems in other susceptible crops, especially in cool seasons. Verticillium wilt is the most common disease affecting okra. The conspicuous symptom is a yellowing of the older leaves, which often develop a burnt appearance, particularly around the margins, followed by wilting of the plant. The only control measures recommended for dealing with this disease are crop rotation and destroying diseased plants.

Powdery mildew can become a significant leaf problem in drier regions. It may result in heavy leaf shed. No chemicals are registered for powdery mildew on okra. Sulphur spray can be used early since a pre-harvest interval of 7 days is necessary.

Ascochyta leaf spot and Cercospora leaf spot

These fungal diseases have been recorded on okra. No definite control measures have been suggested, but spraying with a registered fungicide may be helpful if either of the leaf spots proves destructive.

Below is the table with the most common fungicides used in Ocra production, the minimum days prior to harvest that can be applied and which diseases can be controlled.

Fungicides used in Okra production

The information in this section is provided for educational purposes only. Product trade names have been used for clarity, but reference to trade names does not imply endorsement by the author; discrimination is not intended against any product. The reader is urged to exercise caution in making purchases or evaluating product information. Label registrations can change at any time. Thus the recommendations may become invalid. The user must read carefully the entire, most recent label and follow all directions and restrictions. Purchase only enough pesticide for the current growing season.

 

Weed control

Whether conventional clean-tillage, strip-tillage, or mulches are employed, it is essential to establish a strategy for controlling weeds in okra to avoid competition and interference with pest management and harvest practices. Early stages of crop development, particularly when seedlings or transplants are small, are critical for weed control. Tractor-drawn cultivators, hand-hoeing, or rototilling may be necessary during the initial stages of crop growth. As the crop begins to shade the soil surface, the necessity for cultivation may decrease.

What are the most common weed species in okra?

Weed species infesting okra include annual grasses, perennial grasses and broadleaf weeds. When the okra and weeds are small, hoeing will kill most small weeds. Avoid throwing too much soil directly against the okra stems because it can increase the fungal incidence and specifically stem rot.

How to control weeds in okra?

Okra is harvested over a long period, and weed control remains important throughout the entire season.

Here are some effective ways to control weeds in okra:

  • Mulching: Apply a layer of organic mulch, such as straw, leaves, or grass clippings, around the okra plants. This will help to suppress weed growth and conserve soil moisture.
  • Hand weeding: Regularly inspect the okra plants and remove any weeds by hand, being careful not to disturb the shallow roots of the okra.
  • Hoeing: Use a hoe to cultivate the soil around the okra plants, being careful not to damage the roots. This can be done every few weeks to prevent weed growth.
  • Herbicides: If manual methods of weed control are insufficient, herbicides can be used to control weeds in the okra field. However, care must be taken to follow the label instructions and avoid spraying directly on the okra plants.

Overall, a combination of mulching, hand weeding, hoeing, and herbicide use can be effective in controlling weeds in an okra field. Removing weeds that could serve as a home for insect pests can help minimize insect-related problems as well.

Few herbicides are registered for weed control in okra fields. Misusing them can damage your crop. Carefully follow the instructions on the label and apply herbicides at the right rate and time.

 

https://extension.uga.edu/publications/detail.html?number=C627

https://www.uky.edu/ccd/sites/www.uky.edu.ccd/files/okra.pdf

https://extension.okstate.edu/fact-sheets/okra-production.html

 

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